An insert type expandable garnish is provided and includes a body part that is inserted into a mounting part of a groove shape formed on the surface of a vehicle. A tension structure part is disposed on the body part to press the body part from the inner bottom surface of the mounting part toward the outside of the vehicle, when the body part is pressed toward the mounting part and inserted into the mounting part. An expandable bracket part protrudes from the body part and is adhered with the mounting part, when the tension structure part presses the body part.